class database()
{
    private $db_host = 'localhost';
    private $db_user = 'root';
    private $db_pass = '';

    function connect()
    {
        // connect to mysql
    }

    function query($sql)
    {
        // use open connection and run database query in $sql
    }

    function close()
    {
        // close active mysql connection
    }
}

class users()
{

    private $username;
    private $whateverblegh;

    function register($username, $password, $salt)
    {
        // this function will register a new user, but it needs to use the MySQL class above to send queries to the database...
    }
}